Shingle-wrap liner for a gun barrel

ABSTRACT

Completely nonmetallic gun tube having excellent hot gas erosion resistance, lightness in weight, and being economical to fabricate, the gun tube liner being made of strips or tapes of double-biased, unidirectionally-oriented, nonwoven fiberglass filaments bonded together with a high-temperature epoxy resin. The strips are wrapped to form the inner liner of the gun barrel, the strips making an angle with the bore of the gun to form an edge grain effect or shingling, which effect results in optimum resistance to gun tube erosion and wherein high deformation under load is provided, and processes therefor.

United States atent Eig 1 Feb. 15,1972

[54] SHINGLE-WRAP LINER FOR A GUN BARREL [72] Inventor: Merrill Eig, Parsippany, NJ.

[73] Assignee: The United States of America as represented by the Secretary of the Army 22] Filed: June 4, 1970 [21] Appl.No.: 57,409

Related U.S. Application Data [62] Division of Ser. No. 756,832, Sept. 3, 1968, abandoned.

[52] U.S. Cl. ..89/15, 42/76 R, 156/195 [51] Int. Cl 1f 17/08, F41f 17/04, F410 21/00 [58] Field ofSearch ..89/14 R, 15, 16; 42/76 R, 76 A;

[56] References Cited UNITED STATES PATENTS 477,763 6/1892 Meixner ..42/76R 2,814,313 11/1957 Tate ..138/144 2,845,741 8/1958 Day ..89/16 2,847,786 8/1958 Hartley et a1. .....89/16 3,517,585 6/1970 Slade ..89/16 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-C. T. Jordan Attorney-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and A. Dubroff [57] ABSTRACT Completely nonmetallic gun tube having excellent hot gas erosion resistance, lightness in weight, and being economical to fabricate, the gun tube liner being made of strips or tapes of double-biased, unidirectionally-oriented, nonwoven fiberglass filaments bonded together with a high-temperature epoxy resin. The strips are wrapped to form the inner liner of the gun barrel, the strips making an angle with the bore of the gun to form an edge grain effect or shingling, which effect results in optimum resistance to gun tube erosion and wherein high deformation under load is provided, and processes therefor.

OF GAS FLOW PATENTEUFEB 15 I972 DIRECTION OF GAS FLOW INVENTOR, MERRILL 'EIG "#-y M15, M v 7; Arromwvs;

SHINGLE-WRAP LINER FOR A GUN BARREL This is a divisional application of my copending application Ser. No. 756,832, filed Sept. 3, 1968, now abandoned, for Method of Making Shingle-Wrap Liner for. a Gun Tube."

The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon.

This invention relates to gun tubes and more particularly concerns mortar barrel tubes which are completely nonmetallic and yet are highly erosion resistant, light in weight, economical to fabricate and dependable in operation.

The desirability of an erosion-resistant gun barrel has long been recognized among the military not only from the standpoint of enhanced logistics but also troop combat efficiency. Other desirable properties which the military have long sought to achieve in a gun barrel comprise the budget and finance considerations of inexpensive manufacture and lightness in weight. The long felt need for a gun barrel characterized by these properties is evidenced by the efforts of prior patentees whose inventions for various and sundry reasons fell short of filling the existing hiatus in the art. Illustrative prior art gun barrels are disclosed in the following patents, among others: U.S. Pat. No. 2,249,899 issued July 22, 1941; U.S. Pat. No. 2,845,741 issued Aug. 5, 1958; U.S. Pat. No. 2,847,786 issued Aug. 19, 1958; U.S. Pat. No. 2,935,913 issued May 10, 1950; and U.S. Pat. No. 3,118,243 issued Jan. 21, 1964. For the most part these patents suggest a composite launcher barrel construction wherein a metal core or liner is jacketed by plastic or resinous glass fibers. The function of the outer jacket material is dictated by considerations of lightness and strength while the selection of the core or liner material is dictated by considerations of resistance to wear and erosion. While the underlying rationale in the construction of the prior art launcher barrels appears sound, other considerations of a controlling nature either have gone unnoticed of have presented difficult problems for which solutions were found wanting. For example, metallic liners by their very nature, are heavy, generally expensive to fabricate, and are not light in weight. Further, metallic liners and the like leave much to be desired insofar as resistance to the eroding effects of hostile gun chamber environments is concerned.

Accordingly, it is a principle object of the present invention to provide a gun barrel which is substantially unattended by the aforementioned disadvantages of the prior art.

Another object of the invention is to provide a nonmetallic lightweight gun barrel characterized by increased life expectancy.

Still another object of the invention is to provide an erosion resistant gun barrel characterized by a complete absence of any metal therein.

Yet another object of the invention is to provide processes for fabricating the above gun barrel.

The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the attached drawings wherein:

FIG. 1 illustrates the formation of my double-bias, unidirectionally oriented, filament strips or tapes, not in section.

FIG. 2 shows how the strips may be readily distorted preparatory to wrapping operations, also not in section.

FIG. 3 shows a single wrap of my distorted strip, and multiple wraps to provide shingling."

FIG. 4 is a sectional view of a mandrel having multiple wraps therearound to effect shingling, and other components associated therewith; and

FIG. 5 is a sectional view of my barrel showing my shingled inner liner with respect to the direction of flow of the hot propellant gases.

Referring to the drawings and more particularly to FIG. 1 thereof, there is shown my double-biased, unidirectionally oriented, nonwoven fiber glass strip 14, made from two identical strips and I2, plied together back to back, each of the strips 10 and 12 having fiber glass rovings disposed at an angle dividual fiber glass filaments comprising the strip to more elastically stretch in the direction of the load, as shown at 16 in FIG. 2, in a manner similar to that of a net fabric. This distortion is necessary in order that the tape may be wrapped at any angle to a mandrel surface to be discussed hereinafter.

The strips are conveniently 1 inch wide, although strips up to 1% inches have been used successfully. The liner need not be a structural member, but should be thick enough, after being machined down to approximately one-eighth to onefourth inch to sustain shock loading or stress discontinuities.

FIGS. 3 shows my tape wrapped around A mandrel 20. The ability of the tape to be distorted is readily apparent from the drawing and is necessary in order that a desired angle B between the tape and surface of mandrel 20 may be achieved.

In the actual fabrication of the inner liner, the mandrel 20 will be made of a material which is readily water soluble, inexpensive, and machineable. Ordinary table salt fulfills each of these requirements. The mandrel may be hollow or solid as shown in FIG. 4. A winding angle starter 22 will be used, made of steel or aluminum, for example, and'presents a face 24 which makes an angle of 20% to the mandrel surface. I have found that 20 /2 is very satisfactory, but angles ranging between about 15 to 60 may be used advantageously in fabricating 81 mm. mortar barrel tubes. In specific applications, the tape may be end wrapped, or approximately to the surface of the mandrel. Such a wrapping may be suitable for mortar barrels in resisting erosion due to the hot gases emanating from the flash holes in the mortar boom which would tend to penetrate the inner liner of the barrel. A rammer 26 has a face 28, which makes an angle with the mandrel surface of 20 /2. This angle will always coincide with the angle formed by the winding angle starter. The rammer is then rammed against the wrappings at periodic intervals to insure compactness and proper angles thereof, formation of the endgrain effect and to provide generally uniform windings.

An important consideration in winding tape 14 around mandrel 20 is to ensure the obtaining of edge grain effect. If not obtained, the beneficial efiects of my shingle wrap will not be fully realized. Consider the drawing of FIG. 5, wherein erosion will occur as a result of an edge grain effect occurring at bore surface 30, or in a plane parallel to the axis of the bore and substantially transverse to the individual shingle wraps 32. In the case of a filament wound structure, however, the entire roving will be exposed to the hostile environment, and with the filaments thus disposed, or parallel to the bore surface, the hot gases produced from ignition or combustion of the propellant would cause erosion to attack the entire exposed surface portion of the windings resulting in gross erosion. It is apparent from the above that my shingle-wrap construction is not subject to any such erosion along the entire filament length, but only at the edges thereof.

In order to densify the inner liner, a nylon shrink tape will normally be wrapped therearound under a tension of approximately 25 pounds per inch width thereof. The tape will normally be wrapped twice around the inner liner with about a 50 percent overlap. The nylon tape may conveniently be about 2 inches wide and about one-sixteenth inch thick, and is of a woven construction and porous, thus serving as an absorbing medium for any excess resin and also permitting any entrapped air and/or volatiles to escape therethrough. The cure cycle for the nylon shrink tape-fiber glass shingle wrap comprises about 2 hours each at about 250, 375, and 435 F. After this cure cycle, the nylon tape will have shrunk about 6 to 7 percent and will have induced an external pressure of about 100 to 200 psi. upon the inner layer. The resultant nylon shrink tape-shingle wrap may now be machined down to a desirable thickness, and at least until all nylon tape is removed.

At this point, the metal breech which houses the firing pin will be bonded to the shingle wrap liner with an epoxy novalak resin, for example, and the entire resultant assembly overwrapped in accordance with the following procedure:

Means are provided for rotating the mandrel about its longitudinal axis while drawing fiber glass strands from a spool riding on a reciprocating carriage which moves from one end of the mandrel to the other. Where the strands are not preimpregnated, means may be provided for coating such strands with resin as they are drawn from the spool to the mandrel. Subsequent windings should comprise, alternate groups or layers of helical and circumferential windings. Preferably, three layers of helical windings at an angle of 201 relative to the mandrel axis follow the initial layer of circumferential 1 windings. While both types of windings provide circumferential strength, the helical windings contribute to strength in the longitudinal direction. The latter looms important where undercuts are contemplated for the purpose of facilitating attachments of the gun barrel to the mortar breech. For example. in the construction of an 81 mm. mortar, it is contemplated that the base plug, preferably metallic, adapted to seat in a baseplate and housing the firing pin will comprise a ballor knob-shaped projection coaxial with and attached to a closure or end cap, the latter having an outer diameter substantially the same as that of the gun barrel to which the base plug is attached. It is further contemplated that the base plug will have a flange projecting from the end gap and forming a coaxial, hollow cylinder of reduced outer diameter, the inner diameter of the cylinder being equal to the inner diameter of the gun barrel. By providing the attachment end of the gun barrel an undercut which will mate with the cylindrical flange of the base plug, proper alignment and seating may be effected and attachment of the gun barrel to the base plug will be facilitated. Accordingly, circumferential windings may be applied. over the aforementioned helical windings until the thickness of the gun barrel is built up to that of the base plug flange. Thereafter, another three layers of helical windings may be applied followed by sufficient layers of circumferential windings to build up to the predetermined gun barrel outer diameter. The wound mandrel can then be rotated in an oven to effect curing and upon completion of the curing operation, finish sizing may be effected by cutting off barrel ends to arrive at the final barrel length and by machining the barrel to arrive at the final outer diameter. The mandrel can then be removed and the undercut to effect mating with the base plug flange may then be made.

Preliminary attachment may thereafter be made advantageously by coating with resin the mating surfaces of the base plug and gun barrel and rigidly holding the mating surfaces in contact while subjecting them to a curing operation. To promote adherence it is desirable to knurl or roughen the mating surfaces prior to coating with resin.

Final attachment of the base plug to the gun barrel preferably makes use of undercuts on the base plug which promote rigidity and strength of adherence. These undercuts comprise annular grooves on the periphery of the base plug and preferably comprise an annular groove on the lateral periphery of the end cap and an annular groove on the neck of the knob-shaped projection adjacent the end cap. A continuous layer of fiber glass cloth impregnated with resin is wound advantageously warp direction parallel to longitudinal axis of barrel about a 6- to 12-inch longitudinal section of the barrel adjacent the end cap and about the end cap almost to the neck of the knob-shaped projection. The fiber glass cloth is then cut and folded in such a manner as to permit it to lie snugly against the domelike surface of the end cap. The circumferential fiber glass windings impregnated with resin are around applied over the fiber dglass cloth to cornpress it around the barrel and end cap and epress the cloth into the angular groove of the lateral surface of the end cap. Additional circumferential windings are made in the region of this angular groove until flush. Repetition of this procedure, with the exception that the windings are carried out helically rather than circumferentially, and that the windings are carried down to tether the end cap and fill the angular groove at the neck of the projection adjacent thereto, is continued until about four alternate layers of cloth and windings are applied. The resultant base-plug-fitted barrel is subjected to a curing operation wherein it is rotated in an oven at an elevated temperature. Additional circumferential strength may be given the adjoining areas by overlaying the last layer of helical windings with two layers of circumferential windings prior to curing.

The curing cycle comprises about 1 /2 hours at about and 250 F. and then about 2 hours at about 400 and 450 F. After this final cure, the mortar gun tube is machined to the desired dimensions and the salt mandrel leached out by ordinary tap water.

Actual field testing of my shingle-wrap barrel, indicates that over 1,000 81 mm. mortar rounds could be fired therethrough successfully. Noticeable erosion did occur however at that portion of the barrel where the hot gases emanate from the mortar flash holes. Longer barrel life may be expected if a suitable refractory or metal insert were affixed to the barrel at this portion.

The fiber glass filaments of the double-biased tape may be made from other materials, such as boron or carbon, for example, or even stainless steel.

Furthermore, it will be readily apparent to those skilled in this art that various modifications and alterations can be made without departing from the scope and spirit of this invention, and the foregoing discussion should not be construed to unduly limit the invention.

1 claim:

1. A gun tube for the use in mortars and the like comprising an inner layer of tightly wrapped turnings of a highly erosion resistant tape to form a bore, said tape being double biased, unidirectionally oriented, and comprising a plurality of nonwoven filaments, each of said tape turnings making a similar acute angle with direction of flow of gases passing through said bore, and

an outer layer of fiber glass wrappings integrally disposed about said inner layer, said inner layer tape and said outer layer wrappings being bonded to itself and to each other with a high-temperature epoxy resin.

2. A gun tube as described in claim 1 wherein all parts thereof are completely devoid of metallic parts.

3. A gun tube as described in claim 1 wherein all filaments are selected from the group consisting of fiber glass, carbon, boron and stainless steel,

wherein said acute angle ranges between about 15 and 60,

and

wherein filaments of each individual tape comprising said double-biased tape make angles of+30 and 30 respectively with the axis of said tape. 

2. A gun tube as described in claim 1 wherein all parts thereof are completely devoid of metallic parts.
 3. A gun tube as described in claim 1 wherein all filaments are selected from the group consisting of fiber glass, carbon, boron and stainless steel, wherein said acute angle ranges between about 15* and 60* , and wherein filaments of each individual tape comprising said double-biased tape make angles of + 30* and - 30* respectively with the axis of said tape. 